Method for controlling a transmission of a vehicle

ABSTRACT

Described is a method for the control of a transmission of a motor vehicle, especially an automatic transmission, with hydraulically activated shifting elements. The shifting elements are shifted to engage or disengage by means of specified pressure pattern (p kab , p kzu ) which have been input into an electronic control unit. In the said method, an applied pressure (p kab ) on a disengaged shifting element, by the release of a force flow generated by a holding pressure (p kab-h ), is reduced to a shift pressure (p kab-sd ) and a transmission input speed of rotation (n t ) experiences a change dependent upon the applied pressure (p kab ) on a disengaged shifting element. An adaption of the pressure pattern (p kab ) of a disengaged shifting element is dependent upon the deviation of an actual release time (T LZ-T ) of the change of the transmission input speed of rotation from a specified release time (T LZ ) of the transmission input speed of rotation, and is designed in such a manner that, the change in speed of rotation of the transmission input speed of rotation (n t ), occurs at a shifting at the preset release time (T LZ ) or in a window of time incorporating that same preset release time (T LZ ).

[0001] The invention concerns a method for the control of a transmissionof a motor vehicle in accord with the concept as more closely defined inClaim 1.

[0002] In the case of known automatic transmissions, gear shifting, iscarried out by, among other names, “overrunning shifting”. In this saidshifting, in the force flow of an input power train of a motor vehicle,a first force-fit clutch is opened in a specified pressure pattern.Simultaneously (or nearly so) a second clutch shifts into a secondopening, this time in a slip condition, by means of an additionalpressure pattern. The pressure pattern of the clutches taking part insaid shifting is specified by an electronic control unit and exercisedon the clutches by electro-magnetic positioning devices.

[0003] In general, where this overrunning shifting is concerned, theapplied pressure on a disengaged clutch is reduced to shift-pressure bya holding pressure dependent upon the fluid filling of an engagedclutch. Because of the lessening of the shift-pressure, the powertransfer capability of the disengaged clutch reduces itself on acontinuing basis, and the transmission input speed of rotation begins toincreasingly deviate from a synchronized speed of rotation of the prioractual gear ratio, i.e. the “old” gear position.

[0004] The time, at which the deviation of the transmission input speedof rotation from the run of the synchronized speed of rotation of theactual gear ratio occurs, is designated as a “release time” and at thesame time represents that instant at which the driver, subjectivelymakes a change in the driving conditions of the of the motor vehicle,namely, gear shifting. This is carried out especially following akickdown, after which the pressure applied on the disengaged clutch isreduced and a take-off drive moment reduces itself, before the true gearshift process for the achievement of the desired gear ratio, i.e., the“new” gear. The synchronization is initiated by means of an increasingpower transfer capability of an engaged clutch in the automatictransmission.

[0005] For the increasing of the quality of shifting, after the releasetime, there is provided a control of a gradient in the transmissioninput speed of rotation which is dependent upon the pressure beingapplied to the disengaged clutch, by means of which, a time span iscreated for a speed of rotation change to approach a synchronizedrotational speed in accord with the desired new ratio change of thetransmission.

[0006] Because of the growing requests for shifting quality and therequirement for spontaneity, the demands on the functionality of thesoftware of the automatic transmission also increase. In order to meetthese demands, the consensus of the practice has now embraced the idea,of placing the release time of the transmission input speed of rotationvery close to the beginning of a shift operation.

[0007] However, in achieving the above goal, a problematical situationarises, in that the said release time wanders away from a set, specifiedtime, during the progress of operation where known automatictransmissions are concerned, as a result of tolerances, scattering, andfurther negative influences, such as, for instance, frictional valueswhich change their characteristics during the time of operation, and/orongoing component wear. As a result, ease of shifting becomes poorer andthe spontaneity of the automatic transmission is impaired. Known effortsto hold the release time of the transmission input speed of rotationnearly constant, are, at least to this date, connected with considerablecosts in labor and money, all leading to no satisfactory results.

[0008] Thus, it is the purpose of the present invention to makeavailable a method, with which the release time can be so adjusted, overthe life time of an automatic transmission, that the said release timeapproaches as nearly as possible the beginning of a shifting action andoccurs at a specified time.

[0009] In accord with the invention, this purpose is achieved with amethod for the control of a transmission of a motor vehicle followingthe principles of Claim 1 or Claim 2 of the claims of this invention.

[0010] With the aid of the invented method, in which an adaption of thepressure pattern of a disengaged shifting element, dependent on adeviation between an actual release time of the transmission input speedof rotation and a specified release time, to this effect, provision ismade, that the change in rotational speed of the transmission input canbe carried out, when a shift is made either at the specified releasetime or within a period of time including the said specified releasetime, in an advantageous manner, the time of the change of thetransmission input speed of rotation, that is to say, the actual releasetime, can be held constant during the entire operational life for thetransmission with the same shifting. Further this can specifically bemade to occur at the start of the shifting, in order to bring about adesired high spontaneity detectable by the driver as well as achieving agood quality of shifting. Thereby, the behavior of the transmissionclosely approaches the driver's wish for capacity. Further, scatteringand tolerances degradation caused by wear of components which wouldnegatively affect the behavior of shifting, can be specificallycompensated for over the said operational life of the transmission.

[0011] Moreover, the invented method offers the advantage, that in thecase of multiple gear changes, that is, a multiplicity of sequentialchanges, a synchronous release time of a second shifting element of asecond shifting can be adjusted to an actual synchronous time of a firstshifting element. This permits that after the synchronous time of thefirst shifting element, no all too long a dead time exists in regard tothe increase of the transmission input speed of rotation. Further, theincrease of the transmission input speed of rotation at the same timeis, to the sensations of a driver, the same as continual.

[0012] Further advantages and developments of the invention arise fromthe claims and from the following description made with the aid of thedrawing, the principles of which are shown by embodiments shown in thedrawing as principles. There is shown in:

[0013]FIG. 1 a simplified set of mutually corresponding, qualitativecurves of the speed of rotation of a transmission with plotted pressurerelations of a disengaged clutch as well as the pressure relations of anengaged clutch, and

[0014]FIG. 2 a program flow chart of an adaption-routine in accord withthe invention.

[0015] The curves of FIG. 1, schematically presented, represent thespeed of rotation of a transmission input, which, in this case is alsothe speed of rotation of a converter n_(t), a pressure pattern p_(kab)of a disengaged shift element, this being, for instance, a disengagedclutch, and as well a pressure pattern p_(kzu) of an engaged switchingelement this being, for instance, a engaged clutch. These namedcomponents relate to a method for the control of an automatictransmission, in the case of which, an adaption of the pressure patternp_(kab) of the disengaged clutch, dependent upon a deviation between anactual release time T_(TZ-T) and a specified release time T_(TZ) of thespeed of rotation n_(t) of the turbine wheel, is so designed, that thespeed of rotation change n_(t) of the turbine wheel is made to occursimultaneously with a gear change (shift) at the specified, presetrelease time T_(LZ).

[0016] The shifting elements are designed as hydraulically activatedclutches, which, in the case of gear shifting, are shifted open orclosed by means of an electronic control apparatus which regulates thepressure patterns shown by curves p_(kab) and p_(kzu). With this saidarrangement, a pressure p_(kab) drops off from the release of a forceflow emanating from a holding pressure p_(kab-h) and acting on ashift-pressure p_(kab-sd), and the speed of rotation n_(t) of theturbine wheel, dependent on the pressure p_(kab) exerted on thedisengaged coupling, brings about such a change.

[0017] The pre-set, specified release time T_(LZ), occurs after a startof the reduction of the pressure p_(kab), said pressure reduction beingeffected by the holding pressure p_(kab-h) countering the shift pressurep_(kab-sd). At this time, during the adaption, the time of a shift isdetermined as that of the actual release time T_(TZ-T), at which thespeed of rotation n_(t) of the turbine wheel based on one of the actualselected transmission gear ratios, that is, the synchronized speedn_(t-synalt) corresponding to the last selected gear, has overstepped athreshold value n_(t).

[0018] The threshold value n_(t-schwell) of the turbine speed ofrotation upon a power shift, lies in excess of a to-be-expected time inthe characteristic pattern of the synchronous speed of rotationn_(t-synalt) of the actual selected gear in the transmission, that is,the selected gear ratio change. When this occurs, the threshold limitappears as a series of values corresponding to the speed of rotationn_(t) of the turbine wheel appears (in FIG. 1) as a straight line,parallel to the curve of the speed of rotation n_(t) of the turbinewheel.

[0019] The numerical quantity of the threshold value n_(t-schwell) isdetermined in accord with the desired sensitiveness of the reaction ofthe adaption and also with consideration of the application at the time.As a result, this quantity can lie, advantageously, in a range of from10 r.p.m. to 50 r.p.m. Obviously, it is a matter for the judgement ofthe expert if this limit is to be set above the here stated range.

[0020] Referring again to FIG. 1, at a defined shift-pressure p_(kab-sd)of a disengaged clutch, the speed of rotation n_(t) of the turbine wheelbegins to climb at a certain slope upward in the direction of asynchronized speed of rotation n_(t-synneu) of the newly targeted gearratio of the transmission to be achieved. As this is done, the actualrelease time T_(LZ-T), is established by means of the intersection ofthe said straight line of the threshold values n_(t-schwell) with theupward inclined line of the speed of rotation of the turbine wheeln_(t).

[0021] In order to execute an easily operating down shifting where agear change ratio of the transmission is done by overrunning shifting,it is necessary, before the clutch to be shifted is brought into thepower flow of the output train, to fill said clutch by means of aquick-fill phase t_(sf). This is carried out along with a successivefilling-compensation phase in such a manner that the clutch to beshifted, upon reaching a speed of rotation criterium, at a time beforethe synchronized speed of rotation n_(t-synneu) of the “new” gear ratioof the transmission has achieved the necessary transmission capability.When this is so carried out, then the desired synchronization of theautomatic transmission has been accomplished.

[0022] For this reason, the speed of rotation n_(t) of the turbinewheel, by the application of the holding pressure p_(kab-h) onto thedisengaged clutch is maintained at the synchronized speed of rotationn_(tsynalt) of the “old” gear ratio and only after the run-out of thisperiod, is the pressure p_(kab), now applied to the disengaged clutch,reduced to the shift-pressure p_(kab-sd).

[0023] By means of the shift-pressure p_(kab-sd) of the disengagedclutch, that is to say, the controllable operation thereof, asimultaneous control of the depicted gradient of the of the speed ofrotation n_(t) of the turbine wheel is carried out. This control enablesraising the speed of rotation n_(t) of the turbine wheel at an optional,or necessary time to the synchronized speed of rotation n_(t-synneu) ofthe “new” gear selection. This synchronized speed of rotationn_(t-synneu) of the said “new” gear selection is, in FIG. 1, that partof the curve of the speed of rotation n_(t) of the turbine wheel, whichadjoins the more central part of the curve of the speed of rotationn_(t) at a more gradual slope, that is, with a lesser incline.

[0024] In FIG. 2 is presented a Program Flow Chart of an adaptionroutine for the acquiring of a constant release time T_(LZ) of the speedof rotation n_(t) of the turbine wheel, wherein, at a first step S1 theadaption routine begins. In a second step S2, a test is carried out, asto whether or not, a shift-command has been issued from the electroniccontrol unit of the automatic transmission. In the case of a positivereply, then, in proceeding to Step 3, first a holding phase isintroduced, in which the pressure p_(kab) applied on the disengagedclutch is lowered to the holding pressure p_(kab-h) by means of anoffset and maintained at that pressure for a specified time-span.

[0025] In a Step 4, which follows Step 3, a shift-pressure phase isstarted, in which the pressure p_(kab) applied to the disengaged clutchis decreased to the shift-pressure p_(kab-sd) In this shift-pressurephase, there is carried out, dependent on the pressure p_(kab) of thedisengaged clutch, a control of the gradient of the speed of rotationn_(t) of the turbine wheel, which, in the curve of the pressure p_(kab)applied to the disengaged clutch, that is, the shift-pressure p_(kab-sd)which is shown in FIG. 1 as a wavy line.

[0026] With the start of the shift-pressure phase, in a step S5 amonitoring of the release time, that is to say, of the actual releasetime T_(TZ-T) begins. In a following step S6 the speed of rotation n_(t)of the turbine wheel and an output speed of rotation n_(ab) is measured.The output speed of rotation n_(ab) is input into the computation of acomputerized transmission input speed of rotation, which is the same asthe turbine wheel speed of rotation, by means of an actual gear ratioi_(ist) in the transmission. From the computed speed of rotation of theturbine wheel, once again the threshold value n_(t-schwell) of the speedof rotation n_(t) of the turbine wheel, the curve of which is designedfor the true release time L_(LZ-T), whereby the threshold valuen_(t-schwell) is greater by the off-set value than the computerizeddetermined rotational speed of the turbine rotational speed.

[0027] In step S7 a check is made, as to whether or not the speed ofrotation n_(t) of the turbine is greater than the threshold valuen_(t-schwell). If the answer is “yes”, the procedure is to the next stepS8, wherein the actual release time T_(LZ-T) is determined and inputinto a reference value for the adaption of the pressure p_(kab) of thedisengaged clutch.

[0028] If the check in the step S7 shows that the speed of rotationn_(t) of the turbine wheel is less than the threshold n_(t-schwell) theflow of action, with a dwell period, is returned to the step S6. Thenfollows anew, a measurement of the speed of rotation n_(t) of theturbine wheel as well as the output speed of rotation n_(ab). Next, inthe step S7 which follows step S6 as before, the examination isrepeated. This small loop between S6 and S7 will keep on until thecriterion of the step 7 is fulfilled, or a break-off limit, such as,perhaps, a maximum number of loopings, is reached.

[0029] In embodiments of the invention, provision can be made, thatinstead of employing the threshold value n_(t-schwell) for thedetermination of the actual release time, an applicable threshold of anacceleration impulse or an appropriate threshold of a speed of rotationgradient, or yet an applicable threshold of a measured differencebetween the speeds of rotation of the shifting elements may be employed.

[0030] The actual release time T_(TZ-T) defined by the adaption routine,is in turn employed for the determination of a correction valueada_(druck). To carry this out, first, in a Step 9, the value of adeviation td_(lz) of the known, actual release time T_(TZ-T) from thespecified release time T_(LZ) is computed. In a subsequent step S10 anadaption value is calculated by means of a specified characteristic linein the electronic control unit, based upon the deviation td_(lz) of thealready determined release time T_(LZ-T) from the specified release timeT_(LZ). The specified release time T_(LZ), as an example, can be fedinto the transmission control, as a characteristics map KF=f(C_(getr),m_(mot), n_(mot), p_(kuppl), . . . ).

[0031] Moreover, the possibility exists, of determining the correctionvalue ada_(druck) in connection with the deviation of the alreadydetermined actual release time from the specified release time T_(LZ) bymeans of a characteristics map. This characteristics map presents afunction of the most different operational parameters of the automatictransmission, for instance, the disengaged clutch. As this is done, inthe dependency, one or more values, such as, transmission temperatureC_(getr), clutch pressure P_(kuppl), motor speed of rotation n_(mot),motor torque m_(mot), is incorporated into the characteristics map.

[0032] The adaption value, in the present described variant of theadaptions routine will be added or subtracted to/from the correctionvalues retained in an adaption memory storage. Continuing with theadaption program, in a Step S11 an examination takes place of thecorrection value ada_(druck) as compared in a positive as well as anegative direction against a specified maximum correction valueada_(druck-max).

[0033] If the evaluation of the Step 11 shows that the determinedcorrection value ada_(druck) is, in its amount, greater than thespecified maximum correction value ada_(druck-max), then, for theadaption of the pressure run p_(kab) of the disengaged clutch, as acorrection value ada_(druck), the specified maximum correction valueada_(druck-max) will be given and input into the adaption memory. Theadaption routine then terminates.

[0034] The differentiating function, i.e. the examination in Step 11 isprovided for the purpose of monitoring the adaption as to itsplausibility, especially in the case of a system with some run-in time,that is a system with a history of high operating time, a one-time“drop-out” because of extraordinary operational situations of theautomatic transmission not to be taken into the evaluation.

[0035] The correction value ada_(druck), that is, the final adaptionvalue, leads to an increase of the shift-pressure p_(kab-sd) of a latershifting in the amount of the correction value ada_(druck), if theactual release time T_(TZ-T) of the expired shifting lies before thespecified release time T_(LZ).

[0036] If, however, by means of the above described adaption, an actualrelease time T_(TZ-T) of the evaluated but expired shifting, lies afterthe specified release time T_(LZ), then this leads to a diminution ofshift-pressure p_(kab-sd) adapted for a later shifting in the amount ofthe correction value ada_(druck), that is, by the computed adaptionvalue.

[0037] The adaption of the pressure curve p_(kab) of the disengagedclutch is realized by means of a change in the shift-pressure p_(kab-sd)of the disengaged clutch. Since the holding pressure p_(kab-h)corresponds with the shift-pressure p_(kab-sd), then the said change ofthe shift-pressure p_(kab-sd) of the disengaged clutch can invoke achange of the holding pressure p_(kab-h) of the disengaged clutch alongwith it.

[0038] In another embodiment of the invention, provision can be made,that the adaption of the pressure distribution p_(kab) of the disengagedclutch, is so designed in dependency of the deviation of the actualrelease time T_(LZ-T) of the transmission input speed of rotation n_(t)from the specified release time T_(LZ), can be so arranged that thechange of speed of rotation of the transmission input speed of rotationn_(t) upon the shifting within an applicable window of time can becarried out at the specified release time T_(LZ).

[0039] The goal of the adaption is, in any case, to adjust the releasetime of the speed of rotation n_(t) of the turbine wheel as closely aspossible to that time, at which, the pressure p_(kab) of the disengagedclutch is reduced by the holding pressure Pkabph to the shift-pressurep_(kab-sd), which is correspondingly, the beginning of the shiftingprocedure.

REFERENCE NUMBERS

[0040] ada_(druck) Correction value

[0041] adak_(druck-max) Maximum correction value

[0042] C_(tr-getr) Transmission temperature

[0043] i_(ist-gear) Actual gear ratio of transmission

[0044] m_(mot) Motor Torque

[0045] n_(mot) RPM of motor

[0046] n_(ab) RPM of output shaft

[0047] n_(t) RPM of turbine wheel

[0048] n_(t-schwell) Set threshold value (turbine)

[0049] n_(t-syn-alt) Synchronized RPM of turbine wheel of a current realset ratio in the automatic transmission

[0050] n_(t-syn-new) Synchronized RPM of turbine wheel in targeted gearratio

[0051] p_(kab) Pressure run of a disengaged shift element

[0052] p_(kzu) Pressure run of an engaged shift element

[0053] p_(kab-sd) Shift pressure of a disengaged shift element

[0054] p_(kab-h) Holding pressure

[0055] p_(kuppl) Clutch pressure

[0056] td_(lz) Deviation of the actual release time from the specifiedset time

[0057] t_(f) Complete compensation phase of the engaged clutch

[0058] t_(sf) Quick full phase of the engaging clutch

[0059] T_(LZ) release time

[0060] T_(TZ-T) Actual release time.

[0061] S1 to s11 step of the adaption routine

Claimed is:
 1. A method for the control of a transmission of a motorvehicle, especially an automatic transmission with hydraulicallyactivated shifting elements, which are shifted into engagement ordisengagement by means of a pattern of pressure (p_(kab), p_(kzu)) whichis preset into an electronic control unit, wherein, a pressure (p_(kab))applied to a disengaged shifting element by the release of a flow offorce from a holding pressure (p_(kab-h)) is reduced to a shift-pressure(p_(kab-sd)) and a transmission input speed of rotation (n_(t)), whichis dependent upon the pressure (p_(kab)) applied to a disengagedshifting element, is subjected to a change, therein characterized, inthat an adaption of the pressure pattern (p_(kab)) of a disengagedshifting element, dependent upon a deviation of an actual release time(T_(LZ-T)) of the transmission input speed of rotation (n_(t)) from apreset release time (T_(LZ-)), is so designed, that the speed ofrotation change of the transmission input speed of rotation (n_(t)) canoccur at a given shifting at the said specified release time (T_(LZ)).2. A method in accord with the concept of claim 1, thereincharacterized, in that an adaption of the pressure pattern (p_(kab)) ofa disengaged shifting element, dependent upon a deviation of an actualrelease time (T_(LZ-T)) of the transmission input speed of rotation(n_(t)) from a preset release time (T_(LZ)) of the transmission driveinput speed of rotation is so designed, that the speed of rotationchange of the transmission input speed of rotation (n_(t)) does occurupon a given gear shifting at the said specified release time (T_(LZ)).3. A method in accord with claim 1 or 2, therein characterized, in thatthe preset release time (T_(LZ)) occurs after a beginning of thereduction of the disengaged shifting element pressure (p_(kab)) to theshift-pressure (_(pkab-sd)) by means of the holding pressure(p_(kab-h)).
 4. A method in accord with claims 1 to 3, thereincharacterized, in that, as an actual release time (T_(LZ-T)), the timeof a shifting is determined to be that time at which the transmissioninput speed of rotation (n_(t)), based on a pattern of a synchronizedspeed of rotation (n_(t-syn-alt)) of the transmission input speed ofrotation of an actual operating gear ratio of the transmission,oversteps a specified threshold value (n_(t-schwell)).
 5. A method inaccord with claims 1 to 3, therein characterized, in that as an actualrelease time (T_(LZ-T)) the time of a shifting operation is determinedas that time at which an acceleration surge of the motor vehicle exceedsa preset threshold.
 6. A method in accord with one of the claims 1 to 3,therein characterized, in that, an actual release time (T_(LZ-T)) isdetermined as that time of a shifting operation, at which a gradient ofthe transmission input speed of rotation (n_(t)) oversteps a presetthreshold.
 7. A method in accord with one of the claims 1 to 3, thereincharacterized, in that an actual release time (T_(LZ-T)) is determinedas that time of a shifting operation, at which a measured change inspeed of rotation at the disengaged shifting element oversteps a presetthreshold.
 8. A method in accord with one of the claims 1 to 7, thereincharacterized, in that, by means of an adaption of the pressure pattern(p_(kab)) of a disengaged shifting element, the shift-pressure(p-_(kab-sd)) is changed.
 9. A method in accord with one of the claims 3to 8, therein characterized, in that by means of the adaption of thepressure pattern (p_(kab)) of a disengaged shifting element, the holdingpressure (p_(kab-h)) of the disengaged shifting element is changed. 10.A method in accord with claim 9, therein characterized, in that thechange of the holding pressure (p_(kab-h)) is carried out dependent uponthe change of the shift-pressure (p_(kab-sd)).
 11. A method in accordwith one of the claims 8 to 10, therein characterized, in that theshift-pressure (p_(kab-sd)) is increased for a later shifting operationby a correction value (ada_(druck)), if the actual release time(T_(LZ-T)) of the evaluated shifting occurs before the preset releasetime (T_(LZ)).
 12. A method in accord with one of the claims 8 to 11,therein characterized, in that the shift-pressure (p_(kab-sd)) isdiminished by a correction value (ada_(druck)) for a later shiftingoperation, if the actual release time (T_(LZ-T)) of the evaluatedshifting occurs after the preset release time (T_(LZ)).
 13. A method inaccord with one of the foregoing claims therein characterized, in that,upon the transition to the shift pressure (p_(kab-sd)) a regulation ofthe gradient of the transmission input speed of rotation (n_(t)) iseffected as dependent upon the pressure (p_(kab)) which is exerted onthe disengaged shifting element.